1. Field of the Invention
The present invention relates to coated tools in which a multilayer coating film is furnished on a base part such as a drill, endmill, indexable insert for milling, indexable insert for turning, metal slitting saw, gear cutting tool, reamer, or tap. The invention relates in particular to coated tools, furnished with multilayer coating films, that are lubricative while maintaining resistance to wear.
2. Description of the Background Art
Forming a monolayer- or multilayer-hard film composed of carbides, nitrides or carbonitrides of titanium, hafnium, zirconium or titanium aluminide on the surface of a base part composed of WC-based cemented carbide, cermet, or high-speed steel, in order to improve the wear resistance and surface-guarding capability of machine tools and wear-resistant tools has been well known to date.
Nevertheless, recent trends such as those listed below are leading to a tendency for tool cutting-edge temperatures in machining to be hotter and hotter, and to ever more severe demands on the characteristics of the tool materials.    (1) From the viewpoint of global environmental protection, dry-work processes that do not employ cutting fluids (lubricants) are being sought;    (2) Work materials are being diversified; and    (3) Machining speeds are being accelerated in order to enhance process efficiency all the more.
In particular, film stability at high temperatures (anti-oxidation properties and bondability with respect to base parts) has of course been a characteristic demanded of tool materials; but in relation to tool life, enhancement of wear-resistance—i.e., film hardness at high temperatures—and lubricating characteristics of film substituting for lubricants have become even more crucial.
To address such issues, the creation of a TiAlSi-based film—(AlxTi1-x-ySiy) (NzC1-z), wherein 0.05≦x≦0.75, 0.01≦y≦0.1, and 0.06≦z≦1—is proposed in Japanese Pat. No. 2,793,773. Through incorporating trace amounts of Si into a film, this technology lends the film favorable anti-oxidation properties and a high degree of hardness, and serves to enhance its anti-wear resistance.
Likewise, the creation of a TiSi-based film—(Ti1-xSix)(C1-yNy)z, wherein 0.01≦x≦0.45, 0.01≦y≦0.1, and 0.5≦z≦1.34—is proposed in Japanese Pat. App. Pub. No. H08-118106. By coating tools with highly hard (Ti1-xSix)(C1-yNy)z, this technology makes tool wear-resistance outstanding even in continuous high-speed machining and serves to prolong useable tool life.
With the foregoing conventional technology have been the following problems, however.
The case with the technology in Japanese Pat. No. 2,793,773 is that aluminum is incorporated into the film, and under high temperatures in excess of 900° C. the aluminum in the film surface takes precedence in binding oxygen, forming Al2O3. The problem thus is that the titanium remaining disperses within the film, forming extremely porous titanium oxides and impairing the wear resistance of the film.
With the technology in Japanese Pat App. Pub. No. H08-118106, the downside of the high degree of hardness to (Ti1-xSix)(C1-yNy)z is the problem that owing to its extreme brittleness, if it is employed in machine tools—especially if employed in interrupted cutting—the cutting edge is liable to chip.
What is more, no study whatsoever regarding the film lubricating qualities that would be an issue in dry working is made in either Japanese Pat No. 2,793,773 or Pat. App. Pub. No. H08-118106.